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Vertically Shot Bullet Landing Speed
Name: David
Status: educator
Age: N/A
Location: PA
Country: N/A
Date: N/A
Question:
In the real world,(not the physics world of no air
resistance), how do I calculate the speed of a bullet that was shot
straight into the air when it returns to Earth. For example, say a
rifle had a muzzle velocity of an M-16, what would the bullet's
speed when it comes straight back down. On the news one sees
celebrations in the Middle East of shooting into the air. Just how
dangerous is that?
Replies:
When falling, every object has a "terminal speed" when falling. If this
were not true, a falling raindrop would be moving fast enough to kill you.
It works exactly the same as a parachute, exactly the same. The only
difference is that the parachute is much wider. A parachute makes things
fall slower because it is much wider. The parachute must push much more air
out of the way as it falls. To know the terminal speed requires much more
information than the fact that it is a bullet. Other factors are: mass of
the bullet, cross-sectional area of the bullet, humidity and density of the
air. Still we can say something. I expect a bullet is heavier than a
raindrop, thus increasing the terminal speed. I also expect that a bullet
is wider than a raindrop, thus slowing it down. Therefore, as a first
estimate, the bullet is probably on the same order of magnitude as a
raindrop. A raindrop falls at about 6 m/s. A bullet would thus fall on the
order of 10 m/s. I would expect it could be as high as 50 m/s.
Dr. Mellendorf
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Update: June 2012
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